Method of making chip scale package with heat spreade

ABSTRACT

A dense semiconductor flip-chip device assembly is provided with a heat sink/spreading/dissipating member which is formed as a paddle of a metallic paddle frame in a strip of paddle frames. Dice are bonded to the paddles by e.g. conventional die attach methods, enabling bump attachment and testing to be conducted before detachment from the paddle frame strip.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional of application Ser. No. 09/028,134,filed Feb. 23, 1998, pending.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to semiconductor device assemblies.More particularly, the invention pertains to a method for producing achip-on-board semiconductor device assembly with a heatspreading/dissipating member, and the device produced thereby.

2. State of the Art

In the design and production of modem integrated circuits (IC), animportant consideration is the dissipation of heat generated in thesemiconductor device. Elevated temperatures may cause irreparable damageto the die and its electrical connections.

Various methods for preventing excessive temperatures in a semiconductordevice have been in use.

Thus, for low-power devices of less than about 1 watt, the metal leadframe itself may be sufficient to dissipate generated heat. Lead frameconfigurations for improved heat dissipation are shown in U.S. Pat. No.5,541,446 of Kierse, U.S. Pat. No. 4,961,107 of Geist et al., and U.S.Pat. No. 5,101,465 of Murphy.

For higher power packaged devices, a metal heat spreader may beincorporated into the package or attached to the outside of the package.Because of the generally low thermal conductivity of polymers, the heatdissipation design is more critical for polymerpackaged devices than forthose packaged in ceramic or metal.

The use of heat spreaders/heat sinks/heat dissipaters in packagedsemiconductor devices are often used to conduct heat to the exterior ofthe devices, either directly or via the leads. A wide variety of such isillustrated in U.S. Pat. No. 5,596,231 of Combs, U.S. Pat. No. 5,594,282of Otsuki, U.S. Pat. No. 5,598,034 of Wakefield, U.S. Pat. No. 5,489,801to Blish II, U.S. Pat. No. 4,024,570 of Hartmann et al., U.S. Pat. Nos.5,378,924 and 5,387,554 of Liang, U.S. Pat. No. 5,379,187 of Lee et al.,U.S. Pat. No. 4,507,675 of Fujii et al., U.S. Pat. No. 4,642,671 ofRohsler et al., U.S. Pat. No. 4,931,852 of Brown et al., U.S. Pat. No.5,173,764 of Higgins III, U.S. Pat. No. 5,379,186 to Gold et al., U.S.Pat. No. 5,434,105 to Liou, and U.S. Pat. No. 5,488,254 to Nishimura etal.

The above-indicated references may be characterized as providing complexdevices requiring difficult and/or costly processes to achieve thedesired heat dissipation. Most of the references are not applicable atall to a high density device attached in a bare state to a substratesuch as a circuit board.

Encapsulation compositions and methods are shown in U.S. Pat. No.4,358,552 to Shinohara et al. and U.S. Pat. No. 5,194,930 to Papathomaset al.

SUMMARY OF THE INVENTION

The present invention comprises a high density semiconductor deviceassembly for electrical connection without wires to a substrate such asa circuit board. In a preferred embodiment, the invention comprises achip-on-board (COB) device with a heat spreader/dissipater on its backside. The active surface on its "front side" may be attached in a baredie state to the substrate by lead bond methods known in the art,preferably by ball-grid-array (BGA) methods which simultaneouslycomplete each of the conductive bonds between die and circuit board.

The present invention also encompasses a "paddle frame" strip for (a)providing a heat spreader/dissipater on each die, (b) supporting thedice for die testing and/or (c) supporting the dice for applyingconductive bumps to the bond pads. The paddle frame strip mayincorporate any number of paddle frames, and preferably has at leasteight paddle frames.

The present invention further comprises a method for producing the highdensity semiconductor device with the heat spreader/dissipater.

The present invention provides significant advantages in the productionof dense semiconductor devices, including enhanced reliability, ease ofproduction, and reduced production costs.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The invention is illustrated in the following figures, wherein theelements are not necessarily shown to scale:

FIG. 1 is a plan view of a portion of a paddle frame and attachedsemiconductor dies of the heat spreading chip scale package of theinvention;

FIG. 2 is a cross-sectional side view of a die bonded to a paddle framein accordance with the heat spreading chip scale package of theinvention, as taken along line 2--2 of FIG. 1;

FIG. 3 is an enlarged perspective view of a semiconductor die bonded toa paddle of a paddle frame, furnished with a ball grid array and excisedfrom the paddle frame in accordance with the chip scale package of theinvention;

FIG. 4 is a side view of a circuit board upon which are reversiblymounted paddlebonded semiconductor dies with ball grid arrays inaccordance with the heat spreading chip scale package of the invention;and

FIG. 5 is a cross-sectional side view of a circuit board upon which arereversibly mounted and resin-packaged, paddle-bonded semiconductor dieswith ball grid arrays, in accordance with the heat-spreading chip scalepackage of the invention.

DETAILED DESCRIPTION OF THE INVENTION

An improved high density semiconductor device assembly is provided bythe present invention which is configured to be electrically attached toa substrate such as a circuit board by array bonding. A series of baresemiconductor devices of the invention may be mounted on a substrate ina closely packed arrangement. The semiconductor device is provided witha heat sink/spreading/dissipating member. Following mounting on asubstrate, the device or plurality of devices may be "packaged" with aprotective polymeric sealer.

The semiconductor device assembly and a method for producing it aredescribed hereinbelow and illustrated in drawing FIGS. 1-5.

With reference to the drawings of FIGS. 1 and 2, a metal strip 10 ofheat conductive material is configured with multiple paddle frames 12.The metal strip 10 has left and right side rails 14, 16 and a series ofsprocket holes 18 in the side rails for precise positioning ofprocessing equipment and a plurality of semiconductor dice 20 which areattached to the strip. Each frame 12 includes the side rails 14, 16,cross-members 26, and a generally centrally positioned metal paddle 22which is attached to the side rails 14, 16 by paddle support bars 24 andto cross-members 26 by paddle support bars 28. A semiconductor die 20,having a first major surface 36 and an opposing second major surface 38,has second major surface 38 attached to a paddle 22 by die attachmethods known in the art. Exemplary of such semiconductor die attachmentmethods is attachment using a layer 30 of electrically non-conductivepolymeric adhesive such as epoxy or polyimide. Alternatively, asemiconductor die attach layer 30 may be electrically conductive. Asknown in the art, a metal filled polymer, an unfilled conductive polymersuch as a silver filled epoxy or polyimide, or a conductive gold-siliconeutectic material may be used. Thus, the die attach layer 30 may beelectrically conductive or insulative, depending upon the circuitconfiguration of the second major semiconductor die surface 38. Thus,for example, the second major surface 38 may be designed to be groundedto a ground plane surface, which may be the metal paddle 22.

The metal paddle 22 acts as a heat spreader/dissipater in the finalsemiconductor device assembly 40. Thus, while the semiconductor dieattach layer 30 may be either electrically conductive or insulative, itpreferably has an enhanced heat conductivity. Where the metal paddle 22comprises a metal layer attached to a polymer layer, the semiconductordie attach layer 30 is attached to the metal surface 48 to enhance heattransfer (see drawing FIG. 3).

Each metal strip 10 with paddle frames 12 may be formed in the samemanner as are lead frames in the art. The number of paddle frames 12which may be incorporated into the metal strip 10 is limited only by thecapability of a manufacturer's machines for semiconductor die attachmentand die excising.

The paddle frame 12 includes the left and right side rails 14, 16 whichare joined by cross members 26. The generally centrally located metalpaddle 22 is supported from the side rails 14, 16 and cross members 26by paddle support bars 24, 28. Generally, no leads for electricalconduction are provided, although one or more of the paddle support bars24, 28 may be used as leads in certain specific instances. No narrow"leads" common in lead frames are required in the paddle frame 12,resulting in greater ease of manufacture and increased reliability.

The paddle frame 12 may be formed of a thin film of metal such asaluminum, silver, copper, or Alloy "42". Typically, the metal paddle 22is sized to completely cover the second major surface 38 of thesemiconductor die 20 and preferably be somewhat larger. The thickness 44of the metal paddle 22 is a function of the quantity of generatedthermal energy, the semiconductor die size, the thermal conductivity ofthe semiconductor die attach material, and whether a packaging materialoverlies the metal paddle 22 in the final product. For generally lowrates of heat generation, the paddle thickness 44 may be the minimumrequired by structural considerations. However, where the heatgeneration rate is very high, it may be necessary to increase the paddlethickness 44 to provide an increased heat sink capacity.

In many cases, the thickness 44 of the metal paddle 22 need only besufficient to support the semiconductor die 20 prior to excision, andfor uniform adherence to the semiconductor die 20. The paddle thickness44 may typically range from about 0.5 μm to about 5 μm, but may varyfrom this range, particularly upwardly for enhancing heat sinkcapability. This range of thickness 44 includes the typical paddlethicknesses of lead frames of the prior art. Paddle frames 12 may beformed and joined to semiconductor dice 20 by tape automated bonding(TAB).

To singulate each semiconductor device assembly 40, the paddle supportbars 24, 28 are excised close to the metal paddle 22 with excisions 50(see drawing FIG. 3).

Illustrated in drawing FIG. 1 is a plurality of semiconductor dice 20with conductive bond pads 32 on the first major surface 36, i.e. the"active" surface. While drawing FIG. 1 shows the conductive bond pads 32along the periphery of the dice, thus limiting the number of bond pads,the invention may be used for dice having a full grid array of bond padsas shown in drawing FIGS. 2 and 3.

In a preferred embodiment, conductive projections 34 such as solderbumps or balls are formed on the conductor bond pads 32, the projectionsenabling "gang" bonding, i.e. flip-chip bonding, of the semiconductordie bond pads to the conductive traces 46 of a substrate 42 such as acircuit board. This is illustrated in drawing FIGS. 4 and 5, which showa plurality of semiconductor device assemblies 40 flipped and bonded tocircuit connections, e.g. conductive traces 46 (see drawing FIG. 5), ofa substrate 42 comprising a circuit board. The internal circuitry withinthe substrate 42 is not shown, being irrelevant to the invention. Thesemiconductor device assemblies 40 may be bonded to a substrate 42 in ahigh density pattern and, being "bare" semiconductor dice 20, take upminimal space. The bonding may be completed by standard "flip-chip"methods, including thermal and/or pressure processes.

Each semiconductor device assembly 40 has a heatsink/spreader/dissipater 52 which was formerly a metal paddle 22 of ametal paddle frame 12. The heat sink/spreader/dissipater 52 has agenerally exposed surface 54 for dissipating heat generated in thesemiconductor device assembly 40.

As depicted in drawing FIG. 5, a sealant material 56 may be applied tothe periphery of a semiconductor device assembly 40 and the space 58between the semiconductor device assembly and the substrate 42. Thesealant 56 seals the semiconductor device assembly 40 to the substrate42 and protects the semiconductor device assembly from moisture, etc.The spaces between adjacent semiconductor device assemblies 40 may bereadily filled with sealant 56. The space 58 may be filled, for example,by injecting sealant material 56 through holes, not shown, in thesubstrate 42. Preferably, surface 54 of the heatsink/spreader/dissipater 52 is largely left uncovered to provide highheat dissipation.

Any sealant material 56 useful in packaging semiconductor deviceassemblies may be used, including e.g. epoxy, polyimide, etc.

A method of producing the semiconductor device assembly 40 includes thesteps of:

1. producing a plurality of semiconductor dice 20 with integratedassembly as a wafer, each semiconductor die 20 having a first majorsurface 36 defined as an active surface with an array of conductive bondpads 32, i.e. input/output (I/O) pads, and a second, opposite majorsurface 38;

2. separating the individual semiconductor die 20 from the wafer;

3. providing a conductive "paddle frame" metal strip 10 with multiplepaddle frames 12, each frame having a heat conductive metal paddle 22connected to side rails 14, 16 and cross-members 26 of the paddle frame12 by paddle support bars 24, 28;

4. bonding a semiconductor die 20 to each metal paddle 22 of the paddleframe metal strip 10 with a thin die attach layer 30 of adhesive oradhesive tape of e.g. epoxy or polyimide. The adhesive die attach layer30 may be provided with enhanced heat conductive properties.Alternatively, the second major surface 38 of the semiconductor die 20may be bonded to the metal paddle 22 eutectically by formation of e.g. agold-silicon eutectic layer 30 or other electrically conductive materialsuch as a specially designed polyimide.

5. conductive projections 34, i.e. balls or bumps (stud bumps) forreflow may be formed on the I/O bond pads 32 of the semiconductor dice20 either prior to or following attachment of the semiconductor dice tothe metal paddles 22;

6. the semiconductor dice 20 may be tested in sequence in strip form,i.e. while the paddles 22 with attached dice are connected to the metalpaddle frame strip 10. A test head (not shown) is placed to maketemporary electrical connection with the conductive bond pads 32 orconductive projections 34 for the conduction of parametric andfunctional tests. The testing may include additional tests typical of"burn-in" testing;

7. the metal paddle support bars 24, 28 connecting the paddles 22 to thepaddle frame 12 are excised to free each semiconductor device assemblies40;

The semiconductor devices 40 so produced are configured for mounting ina "flip-chip" configuration, i.e. face down on a substrate 42 such as acircuit board, e.g. by reflowing under heat and/or by pressure or othermethods as known in the art.

The metal paddle 22 attached to the second major surface 38 of eachsemiconductor die 20 comprises a heat sink/spreader/dissipater 52 whichprevents overheating of the semiconductor device assembly 40 (a) duringtesting (including burn-in), (b) during mounting on the substrate 42,(c) during packaging, and (d) in actual operation.

Following attachment to a substrate 42 such as a circuit board, thesemiconductor device assembly 40 may be sealed with an electricallyinsulating sealant material 56 to produce a partially encapsulatedpackage. The exposed surface 54 of the heat sink/spreader/dissipater 52is preferably left largely uncovered, or is only thinly covered with thesealant material 56. The sealant may be any of the polymeric materialscommonly used for packaging, including those used for "glob-top".Examples of such materials are epoxy resins and polyimides.

The invention is particularly applicable to high density integratedcircuit semiconductor device assemblies 40 having a large number ofinterconnections, i.e. conductive bond pads 32. Such devices may producesignificant quantities of thermal energy which, if not removed, may leadto destruction of the integrated circuit. The bare semiconductor dice 20of the invention may be densely mounted on a substrate 42 and thensealed by introducing a sealant material 56 between the substrate andsemiconductor dice to surround the electrical connections and the firstmajor or active surfaces 36 and edges 60 of the semiconductor dice 20.

Major advantages of the invention are as follows:

1. The ease of device handling is enhanced. The semiconductor dice 20are fixed to the unseparated paddles 22 of the "metal paddle frame" 12during the test process and each semiconductor device assembly 40 can behandled without touching the semiconductor die. Once the semiconductordevice assembly 40 is separated from the paddle frame 12 by excision ofthe metal paddle support bars 24, 28, the paddle 22 becomes a heatsink/spreader/dissipater 52, and the device may be handled and supportedsolely thereby.

2. Current methods of lead frame production may be used to produce thepaddle frame metal strip 10. The paddle frames 12 are much simpler indesign than lead frames, there being few or no electrical leads.

3. Semiconductor dice or multiple chips 20 may be mounted on a singlepaddle frame metal strip 10, using equipment widely used by devicemanufacturers. Thus, reliable attachment of the semiconductor dice 20 tothe metal paddles 22, testing (and burn-in) of the dice, separation ofthe paddle mounted semiconductor dice from the paddle frame metal strip10, and mounting of the semiconductor dice on a substrate 42 may beeasily accomplished using well-developed and common assembly equipmentand methods. The readily aligned semiconductor die attach apparatus,test head, and lead excision apparatus enable accuracy and ease ofoperation in the device assembly.

4. The heat sink/spreader/dissipater 52 of the invention results inbetter temperature control and increased reliability of thesemiconductor device assembly 40.

5. Use of known technology and equipment results in a lower assemblycost. No additional specially-designed equipment is required.

6. A dense chip-size bare semiconductor device assembly 40 of lowprofile is produced for dense attachment to a circuit board or othersubstrate 42.

It is apparent to those skilled in the art that various changes andmodifications may be made to the smiconductor die with heatspreader/dissipater and the novel method of manufacturing, testing andinstalling the semiconductor die of the invention as disclosed hereinwithout departing from the spirit and scope of the invention as definedin the following claims.

What is claimed is:
 1. A method for manufacturing a semiconductor deviceassembly, comprising:providing a semiconductor die having an activesurface having a plurality of bond pads thereon and an opposing secondsurface; providing a metallic paddle frame having left and right siderails and a paddle suspended between said side rails for receiving saidsemiconductor die; providing a plurality of conductive projections onsaid plurality of bond pads for connection to a substrate; attaching theopposing second surface of said semiconductor die to said paddle; anddisconnecting said paddle and semiconductor die attached thereto fromsaid metallic paddle frame.
 2. The method of claim 1, furthercomprising:testing said semiconductor die for electrical propertieswhile said paddle is suspended between said side rails of said metallicpaddle frame.
 3. The method of claim 1, further comprising:wherein saidsubstrate includes a printed circuit board having a plurality ofcircuits thereon; and connecting said plurality of bond pads of saidsemiconductor die t o said plurality of circuits of said printed circuitboard.
 4. The method of claim 1, wherein said semiconductor die isattached to said paddle by an electrically non-conductive adhesivematerial.
 5. The method of claim 4, wherein said non-conductive adhesivematerial comprises a polymer.
 6. The method of claim 4, wherein saidnon-conductive adhesive material comprises one of polyimide and epoxy.7. The method of claim 4, wherein said non-conductive adhesive materialcomprises a polyimide tape.
 8. The method of claim 1, wherein saidopposing second surface of said semiconductor die is attached to saidpaddle by an electrically conductive material.
 9. The method of claim 8,wherein said electrically conductive material comprises a eutecticmaterial.
 10. The method of claim 9, wherein said eutectic materialcomprises a goldsilicon eutectic layer.
 11. The method of claim 8,wherein said electrically conductive material comprises a polymer filledwith conductive particles.
 12. The method of claim 1, furthercomprising:providing conductive bumps on said plurality of bond pads onsaid active surface of said semiconductor die for conductiveball-grid-array connection to said substrate.
 13. The method of claim 1,further comprising:providing a substrate having a plurality of circuitsthereon; and connecting said plurality of bond pads on said activesurface of said semiconductor die by a conductive ball-grid-arrayconnection to said plurality of circuits on said substrate.
 14. Themethod of claim 13, wherein said substrate is connected to saidplurality of bond pads on said active surface of said semiconductor dieby said conductive ball-grid-array connection to said substrate.